The present invention relates to pressure plate filters with horizontally arranged filter plates.
Pressure plate filters have been in use for many years in a wide range of applications. When reliable discharge of dry filter cake is required it is often desirable to use a pressure plate filter having horizontally arranged filter plates as it allows the pressure within the filter vessel to be reduced without danger of filter cake falling from the surface of the filter plate. There are a number of commercially available pressure plate filters having horizontally arranged filter plates. For example, BHS SONTHOFEN of Germany produces a pressure plate filter having horizontally arranged filter elements with downward sloping filtration surfaces. Filter cake is shaken off the plates by oscillating the plates, causing the filter cake to slide off the filter plates. Another horizontally arranged filter is the FUNDA filter, available from Chemapec Inc. in the United States, in which dry filter cake is removed from horizontal filters by centrifugal force resulting from rotation of the filters.
The above-mentioned filters each have a conical section at the lower portion of their respective pressure filter vessels for collecting filter cake, and each requires a relatively large annular gap between the filter plates and the vessel wall for the filter cake to fall through. These empty spaces reduce the wash efficiency (wash efficiency being the amount of wash liquor used during a wash cycle relative to the amount of filter cake) of the filters as they are spaces which must be filled with wash liquor that is superfluous to the washing process.
The conical section provided in the above filters is used to direct filter cake towards a discharge opening located at the base of the filter vessels. However, the increasing diameter of the conical section causes the upward velocity of slurry introduced to the vessel to decrease as it rises up in the cone, which can result in large particles suspended in the slurry falling backwards into the base of the cone. In some cases, the large particles remain in the conical section and form a plug of wet solids in the lower portion thereof. Such an accumulation of solids impedes the discharge of the dry filter cake. The slurry or suspension that is left in the conical section at the end of the filtration cycle is referred to as the "heel". The "heel" left in the above filters is relatively large and as a result can be troublesome and time consuming to filter properly.
Another example of a horizontal pressure plate filter is disclosed in U.S. Pat. No. 3,494,467 issued Feb. 10, 1970 to D. Paisley and M. Schroeder which discloses a horizontal leaf dry cake discharge filter in which the entire filter housing is rotated by 90.degree. in order to discharge cake from the filter elements. A screw feed within the housing is used to collect the discharged filter cake. Such a configuration requires enough room to allow the housing to rotate 90.degree.. The housing also includes volumes which must be filled with wash liquor that are superfluous to the process.
It is thus desirable to provide a pressure plate filter with horizontally arranged filter plates which is cost effective to manufacture and operate, which provides an increased wash efficiency by minimizing empty spaces, and which reduces the amount of "heel" in the filter vessel.